- Deletion including the oligophrenin-1 gene associated with enlarged cerebral ventricles, cerebellar hypoplasia, seizures and ataxia. Tentler, D., Gustavsson, P., Leisti, J., Schueler, M., Chelly, J., Timonen, E., Annerén, G., Willard, H.F., Dahl, N. Eur. J. Hum. Genet. (1999)